On my 1985 F150 (carbed 302, Duraspark II conversion, AOD), there is a ported vacuum switch located on top of the thermostat housing or elbow. There are three different hookups; the top one is plugged, and the other two has a small length of hose that connects the bottom two together. The truck runs fine like this, but someone obviously did some sort of botch job, and it looks ridiculous as it is. I thought about just simply removing the ported vacuum switch and putting a pipe plug in there, but first I would like to know the reason Ford put it there and what this switch did exactly.

One by one, starting from the top port, can someone tell me where these three lines originally connected to?

 

If we assume this is your emissions setup(there are several for your year and engine),
http://www.autozone.com/images/cds/g...3d800ce68c.gif

then it's either controlling a "TCP" on the carb(I cannot find what this is, probably Temperature Control "something") or it's the vacuum switch that controlled the heat riser valve.

 

There are three different types, and they all look similar.

Official Ford Nomenclature:

Distributor Vacuum Control Valve (12A091-type three)

Coolant Temperature Vacuum Control Switch (8A564)

EGR Vacuum Control Valve Assy. (9D473)

Because there are so many, and they all look the same...if the part is genuine Ford it will have a FoMoCo ID number on it.

Examples: D5DE-(9D473)-B1A / D7OE-8A564-A1A / D5VE-(12A091)-AA

The ID number is usually in between the ports, or on the reverse side.

If genuine Ford, each port will be marked with a individual letter...which points to where the vacuum lines run to.

 

I've got the same engine and the same valve. From what I have learned (and can tell), this is a coolant temperature control valve (labeled VCV on the vac diagram). There is a passageway in the intake manifold that ports exhaust under the carb, and a flapper valve that controls it (the top of the valve is visible on the passenger's side of the intake manifold - it should have a vacuum nipple on it if it isn't connected to anything). When the engine is cold, the switch ports vacuum to the valve, the valve opens, and the exhaust flows under the carb and warms it. When the engine coolant reaches a certain temp (maybe 100 degrees??), it blocks the vacuum and the flapper valve closes. Apparently this makes the engine run better in cold weather when the carb is prone to freeze. (There are actually two flapper valves connected in series, one is on the driver's side exhaust manifold, and is labeled EXH HCV on the vac diagram. The other, the one I'm talking about here, is on the intake manifold, and is labeled INT HCV)

It's also worth noting, that there are three ports on the valve in my truck, and one is plugged, although the vacuum diagram indicates that the plug is actually a filter.

I'm still investigating, but there are at least two more of these VCV's in my VAC system, both of which are at the rear driver's side of the engine. I cannot tell yet if they sit in coolant or not - but it appears they do. I've got the motor out of the truck right now - i've been meaning to take a closer look at them. I'll try to do that tonight and try to update the post.

 

I was also wondering if I could plug the thermostat housing where the vac trees are will it cause it to overheat all my smog stuff removed with vac advance to carb on a 351m

 

If you aren't using the ported vacuum switch you can safely remove it. Neither of my M's have the switch and that port is plugged.

 

Thread dredge award of the week!

It won't effect the operation of your thermostat.
If there is nothing connected to it, go ahead and replace it with a plug.

 

Of the year I'd say. But you have to give rdz credit - he obviously did research instead of just starting a new thread.

 

The year is young.

Rep's for using the search function!

 

Thanks for the help guys looked at alot of posts no one gave a definite answer

 

I've got two unused vacuum switches. Nearly all my emissions stuff was removed before I got the truck. I was wondering if you recall the thread pitch or part numbers for the plugs you used. Trying to clean up the mess in the engine bay.

 

The ones in my 351M's thermostat housing are 3/8-18 pipe.

 

Cool, I'll fab myself some. Love having a small machine shop at my disposal.

 

I love that as well. But why not commercially-available pipe plugs? Mine were the brass ones that stick out a mile, but I'll go back with some with recessed drive, either hex or 3/8".

Anyway, if you make some please post what you've done as I may want to steal shamelessly.

 

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